Sintered silver-cadmium oxide contact members are useful for high electric current applications. Sintered silver-cadmium oxide contact members are formed by blending fine particle size silver and cadmium oxide powders into a uniform mixture. This mixture is pressed into a compact suitable for sintering. The sintering step is conducted by heating the pressed compact to a temperature of about 900.degree. C and holding the material at that temperature for about one hour.
Difficulties experience in attaining densification during the sintering of the two materials are largely attributable to the morphology associated with such sintered materials where pores and cadmium oxide aggregates are present in the silver grain boundaries. Because of the dissociation of cadmium oxide during sintering, the insolubility of cadmium oxide in the silver matrix and the continual growth of cadmium oxide aggregates through an evaporation/condensation mechanism, the maximum density of the silver-cadmium oxide contacts is typically less than theoretical.
During the sintering, the two major processes-the normal diffusional process for silver-silver particle bonding and the opposing force to densification exerted by the cadmium partial pressure are operating simultaneously. Since the temperature dependence of the silver diffusional force is less than that of the cadmium partial pressure, there exists a temperature above which sintering is seriously impeded by the cadmium pressure. Moreover, the cadmium vapor pressure generated in a closed pore during sintering is probably higher than in an open environment due to a decrease in the oxygen partial pressure through diffusion of oxygen into silver grains.
The resultant difficulties in attaining good densification of the two materials create the excessive growth of cadmium oxide aggregates in the sintered body which in turn accompanies inferior arc erosion resistance which is an important attribute of a good electrical contact.